1. Technical Field
This disclosure relates to a cooling apparatus such as a Peltier apparatus applying a cooling element such as a Peltier device, a cooling method, a program, a computer readable information recording medium such as a ROM, and an electronic apparatus such as an image forming apparatus in which the cooling method is applied.
2. Description of the Related Art
Conventionally, a cooling apparatus applying a Peltier device, having a reduced size and including no mechanical moving parts, is therefore employed for avoiding temperature rise otherwise occurring due to heat generated by circuit devices and properly controlling a temperature environment, within an apparatus in which IC devices, electronic devices, electrical components or such are assembled within a narrow space inside of a housing (such an apparatus being referred to as an ‘electronic apparatus’ hereinafter). For example, Japanese Laid-open Utility-Model Application No. 5-28657 discloses an example in which such a cooling apparatus is applied for cooling a recording sheet in a printer, a facsimile machine or such.
The Peltier device is a device which has a configuration in which PN thermoelectric semiconductors are bounded by cupper electrodes and in which, when a direct-current voltage is applied, heat movement occurs via the bonded surfaces, and thus, a cooling part occurs on one side and a heat generating part occurs on the other side. A common way of driving the Peltier device in the relate art is such that power supply is made by a constant voltage or in a PWM manner. For example, when the Peltier apparatus (device) is applied in an image foaming apparatus such as a copier, a printer or such, a constant DC voltage is supplied from a power supply unit as it is, or, power supply is made in a PWM manner with the use of an FET switching device or such. In a case where a temperature of a control target is measured by a sensor, the power supply is turned on or turned off in such a manner that the detected temperature is controlled for a target value. Specifically, in the PWM operation, setting of a duty is changed so that a cooling performance is changed accordingly.
However, as well known in the art, in a case where the Peltier device is driven in the manner that the power supply is turned on or turned off as mentioned above, degradation of the Peltier device may be accelerated when a temperature difference between a heat generating surface and a heat sink surface of the Peltier device occurs sharply as a result of a large change in the driving voltage being applied. As a result, the life of the Peltier device may be shortened.
Japanese Laid-open Patent Application No. 11-289111 discloses a method for solving this problem of degradation of the Peltier device. In this method, an analog feedback control circuit is provided by which a detected temperature obtained from a sensor which detects a temperature of a cooling target is fed back in such a manner that a power supply voltage to the Peltier device may change in proportion to the detected temperature. Further, in this method, a delay circuit is provided such as to provide a delay when the detected temperature is fed back. Thanks to operation of the control circuit having such a configuration, the driving voltage applied to the Peltier device is prevented from being rapidly changed, the input voltage is prevented from being changed in a step manner also in the PWM operation, and thus, a temperature change on the cooling surface generated in the Peltier device occurring in response to a temperature change in the cooling target is controlled to occur gently. Thus, the cooling operation is carried out in such a manner that rapid heat shrinkage in the Peltier device can be avoided, and thus, performance degradation can be reduced.
However, in the above-mentioned prior art method, the analog feed back control circuit delays the detected temperature of the cooling target as mentioned above. Accordingly, a relatively long time may be required (that is, a follow-up speed is slow) until the applying driving voltage is stabilized into a proper value upon turning-on of the Peltier device (at a time of rising up) or turning-off of the Peltier device (at a time of decaying down), or in response to a sharp temperature change occurring in the cooling target. Therefore, for a case where a subsequent step is executed after this stabilization, processing delay may occur. Further, since this method employs the analog circuit, it may be difficult to carry out adjustment of the performance of the control circuit including adjustment of the sensor for detecting the temperature. the delay circuit, and so forth. As a result, it may be difficult to optimize the circuit performance for each particular apparatus.
Further, in the above-mentioned prior art method, the configuration is provided such that, as mentioned above, the temperature change caused on the cooling surface of the Peltier device is controlled to occur gently. However, the essential factor causing the relevant performance degradation is a sharp occurrence of temperature difference between the heat generating surface and the heat sink surface of the Peltier device. The control in the above-mentioned prior art method may not be directly directed to avoiding this sharp occurrence of temperature difference between the heat generating surface and the heat sink surface of the Peltier device. Accordingly, this method may not be sufficiently effective to solve the relevant problem.